1. Field
This disclosure is concerned generally with collection and separation systems for whole blood and specifically with a blood component separation system that can be partially automated.
2. Prior Art
Whole blood is commonly separated into its major components of less dense plasma and more dense red blood cells (RBCs) by first drawing the whole blood into a plastic bag known as a donor or primary bag. The bag's contents are then centrifuged under controlled conditions to result in a lower, more dense portion of packed RBCs and an upper less dense plasma portion, which may be rich in platelets (platelet rich plasma or PRP).
The donor bag is typically connected by plastic tubing to one or more satellite bags into which separated blood components (e.g. the PRP) may be expressed by external manipulation for further processing or use.
The above system for separating blood into its major components has remained virtually unchanged since the 1950's when plastic blood bags were introduced commercially on a large scale.
The classical method of preparing platelet transfusion products from whole blood collections consists of initial centrifugation of whole blood in a plastic blood bag at relatively low centrifugal force to separate most of the PRP from the red cells. The PRP is commonly expressed into an attached satellite blood bag. This is followed by centrifugation of the PRP in the satellite bag at relatively high centrifugal force to form a lower sediment of platelets and an upper platelet poor plasma (PRP). The sedimented platelets are in the form of a pellet or "button" which is resuspended in a small volume (50-60 mL) of donor plasma to give the platelet concentrate.
With good technique, about 2/3 of the platelets in a whole blood collection unit are recovered in the platelet concentrate. This is equivalent to about 8.times.10.sup.10 platelets per concentrate. However, achieving this yield of platelets requires strict attention to centrifugation protocols, frequent calibration of the centrifuges, and operator diligence. The fact that the minimum standard for platelet yield is only 5.5.times.10.sup.10 per concentrate attests to the operator-dependent nature of this procedure.
Recently, some transfusion services in Europe have begun to investigate and in some cases employ an alternate method of platelet preparation, specifically preparation from buffy coat. In this procedure the initial centrifugation of whole blood is performed at relatively high centrifugal force to form an upper layer of relatively cell-free plasma, an intermediate buffy coat layer containing platelets and leukocytes, and a lower layer of red cells.
The buffy coat plus either a small volume of plasma or a synthetic medium is then centrifuged at low centrifugal force to separate platelet concentrate (upper layer) from residual red cells and leukocytes. Data suggest that platelets prepared in this fashion are of improved quality, presumably because platelet activation that would otherwise occur during the pelleting step of the PRP centrifugation method is avoided.
The original work on buffy coat platelets was done at the Dutch Red Cross. Referred to as the Amsterdam method, it employed a standard quadruple plastic bag system. After centrifugation of blood and removal of plasma from the main bag, the buffy coat layer was transferred to an empty connected satellite bag and then processed to platelet concentrate. Using this method, Pietersz et al. (Vox Sang 1985; 49:81-85) found a mean of 7.2.times.10.sup.10 platelets per concentrate; the volume of blood collected in this study was 500 mL. Kretschmer et al. (Infusionstherapie 1988; 15:232-239) found a mean of 6.3.times.10.sup.10 platelets per concentrate from 450 mL blood collections.
The Amsterdam method, while apparently giving respectable platelet yields, was cumbersome and labor-intensive. The buffy coat transfer step required the operator to massage the bag to prevent hang-up of the "sticky" buffy coat layer. These manipulations might influence platelet function and release of granulocyte enzymes. There was also no way to control the volume of buffy coat removed.
Other efforts to improve platelet separation procedures or at least make it less burdensome are known. For example, U.S. Pat. No. 3,911,918 to Turner discloses a blood bag having an hour glass shape. That bag has a top portion for plasma, a bottom portion for RBCs and a middle portion for platelets and white blood cells. The hour glass shape is said to help position clamping or sealing devices at the juncture of the separated components after whole blood in the bag is centrifuged. This system has not been used on any significant commercial scale to date.
In U.S. Pat. No. 4,608,178 to A. S. Johansson and C. F. Hogman there is disclosed a "top/bottom" with which the upper and lower portions of separated blood components can be simultaneously expressed from a specially designed bag which leaves behind in the bag the intermediate portion known as buffy coat. The expression of that system is controlled by a pressure plate on the bag and sensors which monitor the position of the intermediate layer such that it remains in the bag while the upper plasma is expressed from a top part and the lower red blood cells are expressed from a bottom part in the bag. Hence, the name top/bottom bag. The sensors in that system assure the simultaneous expression of the top and bottom components.
The above described systems are fairly recent and it is not clear yet whether those systems will in time replace existing blood separation systems based on the use of a relatively simple unmodified donor bag.
However, the systems do offer new ways to prepare platelets (contained in the intermediate or buffy coat portion). The patent to Johansson and Hogman show how to do this in a semi-automated manner. Hence, it potentially represents a semi-automated way to prepare platelets.
In an effort to overcome problems associated with the Amsterdam method, Johansson and Hogman (see above-cited patent) developed the bag system with the top and bottom drainage of the primary bag and a sensor device which allowed partially automated blood separation. Kretschmer et al. used that type of system to prepare platelet concentrates from buffy coats and found a mean of 6.7.times.10.sup.10 platelets per unit.
We have now found a novel alternative to the above described automated system, the details of which are described below.